1、題目

Given a string containing just the characters?'(',?')',?'{',?'}',?'['?and?']', determine if the input string is valid.

The brackets must close in the correct order,?"()"?and?"()[]{}"?are all valid but?"(]"?and?"([)]"?are not.

?

2、思路

用stack來實現，左邊的進棧，如果是右邊的出棧，發現沒有或者不匹配就返回false

3、代碼實現

public class Solution {public boolean isValid(String s) {if (s == null || s.length() == 0) {return false;}char chars[] = s.toCharArray();Stack<Character> stack = new Stack<Character>();for (int i = 0; i < chars.length; ++i) {if (chars[i] == '(' || chars[i] == '{' || chars[i] == '[') {stack.add(chars[i]);} else {if (!stack.isEmpty()) {Character value = stack.pop();if (chars[i] == ')') {if (value != '(') return false;}if (chars[i] == '}') {if (value != '{') return false;}if (chars[i] == ']') {if (value != '[') return false;}} else {return false;}}}return stack.isEmpty();} }
?

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